1. Field of the Invention
The invention relates to a lighting control technique of a light source for reading an original in an image forming apparatus having both a copying function and a printing function.
2. Related Background Art
Hitherto, an image forming apparatus with a system construction as shown in FIG. 2 has been known. In the system of FIG. 2, it has a host computer 2103, a printer control unit 2005, and an engine control unit 2003. The host computer 2103 and printer control unit 2005 are directly connected or connected via a network 2105.
The printer control unit 2005 performs a control such that image data of various describing formats such as a PDL (Page Description Language) and the like transmitted from the host computer 2103 is converted into image data of a raster format. The engine control unit 2003 controls a printer engine (not shown) on the basis of the image data transmitted from the printer control unit 2005 via a video interface (I/F) 2104, thereby forming an image onto a recording paper.
As shown in FIG. 27, there has also been realized an image forming system such that by adding an image readout apparatus 101 to the system of FIG. 2 and connecting the image readout apparatus 101 to the host computer 2103 via the network 2105 or directly, image data read out by the image readout apparatus 101 can be printed out by the image forming apparatus.
Further, as shown in FIG. 28, a system such that an image readout apparatus (reader unit) 2601 is directly added to the image forming apparatus and the printing function and the copying function are realized is also known. That is, in the system of FIG. 28, data as a target of printing transmitted from the host computer 2103 is converted into a raster format by a controller unit 2602 and transferred to the engine control unit 2003 via a selector unit 2603, so that it is printed out. Original image data read out by the reader unit 2601 is transferred to the engine control unit 2003 through the selector unit 2603 and is subjected to a copying process. In this instance, the selector unit 2603 controls so as to transfer the data from either the controller unit 2602 or the reader unit 2601 to the engine control unit 2003 in accordance with the printing mode or copying mode.
However, in case of the apparatus having the construction such as to realize both the printing function and the copying function as shown in FIG. 28, a time that is required from the generation of an output request to timing when the image signal is actually outputted in the copying mode is much longer than that in the printing mode. There is also a problem such that if the customer tries to shorten such a delay, the costs rise.
That is, in printing, image data to be transmitted has already been held in a memory of the host computer 2103 or controller unit 2602. Therefore, when an output request is issued, the output operation can be started with only a waiting time until a ready status of the printer engine is guaranteed or, if the printer engine is in an output possible status at a point when the output request is issued, the output operation can be started without a waiting time. On the other hand, in copying such that the reader unit 2601 to read an original synchronously with the printer engine has to be made operative, a waiting time until the ready statuses of both the reader unit 2601 and printer engine 2002 are guaranteed is necessary. That is, in copying, the reader unit 2601 certainly needs a waiting time until an original reading operation is started after the output request was issued. For example, a necessary lighting time of a light source is considered as a factor of the waiting time.
If the necessary lighting time of the light source of the reader unit 2601 is shorter than the waiting time until the printer engine enters the ready status, the waiting time in copying can be made identical to that in printing. However, the necessary lighting time of the light source is generally prolonged in proportion to an accumulated lighting time. Therefore, in copying, a time that is required from the generation of the output request to timing when the image signal is actually outputted is slower than that in printing. To eliminate such a delay, the light source has to be exchanged to a new one before the necessary lighting time of the light source is longer than the necessary time until the printer engine enters a ready status in spite of a fact that there is enough time for the life of the light source. However, such a method results in a remarkable increase in costs.